Semiconductor integrated circuit device

ABSTRACT

Interconnections are formed over an interlayer insulating film which covers MISFETQ1 formed on the principal surface of a semiconductor substrate, while dummy interconnections are disposed in a region spaced from such interconnections. Dummy interconnections are disposed also in a scribing area. Dummy interconnections are not formed at the peripheries of a bonding pad and a marker. In addition, a gate electrode of a MISFET and a dummy gate interconnection formed of the same layer are disposed. Furthermore, dummy regions are disposed in a shallow trench element-isolation region. After such dummy members are disposed, an insulating film is planarized by the CMP method.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of U.S. Ser. No.10/619,039, filed Jul. 14, 2003, which is a Continuation of Ser. No.10/075,246 filed Feb. 15, 2002, now U.S. Pat. No. 6,664,642, which is aContinuation of Ser. No. 09/846,260, filed May 2, 2001, now U.S. Pat.No. 6,433,438, which is a Divisional application of Ser. No. 09/050,416,filed Mar. 31, 1998, now U.S. Pat. No. 6,261,883. This application isrelated to application Ser. No. 10/926,142, filed Aug. 26, 2004, whichis a Continuation of application Ser. No. 10/619,039, filed Jul. 14,2003.

BACKGROUND OF THE INVENTION

This invention relates to a semiconductor integrated circuit device andto a fabrication process thereof, and more particularly, the inventionrelates to a technique which is effective when applied to asemiconductor integrated circuit device, which is fabricated by aprocess including a planarization step using the CMP (ChemicalMechanical Polishing) method.

To satisfy the continuing tendency to decrease the minimum processingsize of a semiconductor integrated circuit device, in an exposureoptical system, an increase in the performance of a stepper is required,which promotes a widening of the aperture size of a lens and ashortening of the exposure wave length. As a result, the focus depth ofthe exposure optical system decreases and even a slight unevenness onthe surface to be processed becomes a problem. Therefore, the accurateplanarization of the surface to be processed becomes an importanttechnical objective for the device process. Furthermore, the aboveplanarization does not aim at the easing of a stepped portion for thepurpose of preventing a short cut of interconnections formed on thestepped portion, but is directed to a global planarization, in otherwords, a complete planarization.

As a surface planarization technique, there are a method of coating anSOG (Spin On Glass) film or a low-melting-point glass by melting it, amethod of heat treatment through glass flow, a self planarization methodadopting a surface reaction mechanism of CVD (Chemical Vapor Deposition)and the like. Owing to the surface conditions, to the heat treatmentconditions being applied or to limitations in processing, in many cases,it is impossible to carry out complete planarization, that is, globalplanarization, using these methods. Therefore, the etchback and CMPprocesses are regarded as promising practical techniques which permitcomplete planarization.

As for the etchback process, the use of a photoresist as a sacrificialfilm, the use of an SOG film and the use of a self-planarization CVDfilm are known, but they are accompanied by such drawbacks as a complexprocedure, a high cost and a lowering of the yield due to production ofparticles. The CMP process has, on the other hand, come to be regardedas an excellent process from an overall viewpoint, because, comparedwith the etchback process, it is more free from the above-describedproblems. Consequently, the CMP process is considered to be mostpromising as a practical technique for effecting complete planarization.

The CMP technique is described in, for example, Japanese PatentApplication Laid-Open No. HEI 7-74175, U.S. Pat. No. 5,292,689 and “1996Symposium on VLSI Technology Digest of Technical Papers, 158–159(1996)”.

SUMMARY OF THE INVENTION

During the investigation of a technique for the complete planarizationof a device surface to which the CMP method is applied, which techniqueis not, however, a known process, the present inventors have recognizedthat there are the following drawbacks.

FIGS. 29( a) to 29(d) are each a cross-sectional view illustrating aplanarization technique using the CMP method which the present inventorshave investigated. For covering an interconnection with an insulatingfilm and then planarizing the insulating film, an interconnection 102 isformed on an interlayer insulating film 101 (FIG. 29( a)); a firstinsulating film 103 and a second insulating film 104, such as SOG, aredeposited to embed a concave portion thereof by the plasma CVD method orthe like using TEOS (Tetraethoxysilane: (C₂H₅O)₄Si) (FIG. 29( b)); athird insulating film 105 is deposited by the plasma CVD method usingTEOS (FIG. 29( c)); and then the third insulating film 105 is polishedby the CMP method for effecting planarization (FIG. 29( d)).

At the present time, in the designing of a layout based on principles offunctional design and logic design, the most important considerationconcerning the pattern of the interconnection 102 has been based onwhether the pattern follows the ordinary layout rule or not, andpolishing properties in the CMP step have not been taken into particularconsideration.

The interconnection pattern is therefore not uniform, being sparse insome places and dense in some places. In the drawing illustrating thetechnique under investigation (FIG. 29( d)), it is seen that theinterconnections 102 are dense in the portion A, while they are sparsein the other region. When CMP polishing is conducted under such a state,that is, a state where interconnections 102 are not disposed uniformly,being sparse in some places and dense in some places, the surface of thethird insulating film 105 cannot be planarized completely. In a regionwhere the interconnections 102 are dense, there appears a difference of0.2 to 0.3 μm in height in the region A and a large undulationinevitably remains on the surface.

On the surface having such an undulation, the processing margin lowersin the subsequent photolithography step or etching step, and it becomesdifficult to satisfy minute processing and heightening requirements ofintegration, which makes it impossible to bring about an improvement inthe reliability of the semiconductor integrated circuit device and alsoan improvement in the yield. In addition, the existence of an undulationrequires the optimization of the process conditions in order to carryout lithography and etching favorably in such a state, and anoptimization of the CMP step also becomes necessary to suppress theundulation to a minimum. The time required for such optimizationsometimes undesirably delays the starting time of the mass-productionprocess.

In the region where the interconnections 102 are disposed sparsely, therecess between the interconnections 102 is not embedded sufficientlywith the second insulating film 104, and so the third insulating film105 must be thicker in order to fill in such a recess completely, whichconsequently causes problems, such as an increase in the polishingamount of the third insulating film 105 and a rise in the step load inthe CMP step, as well as an increase in the step load, such as a longdeposition time, of the third insulating film 105.

An object of the present invention is to completely planarize thesurface of a member which has been polished by the CMP method.

Another object of the present invention is to provide a technique whichcan improve the processing margin in the photolithography and etchingsteps, thereby to achieve minute processing and an increasedintegration, while, at the same time, improving the reliability andyield of the semiconductor integrated circuit device.

A further object of the present invention is to facilitate the start ofthe process.

A still further object of the present invention is to reduce the amountof polishing of a member to be polished by the CMP method and todecrease the load and time of the polishing step, thereby improving thecost competitive advantage.

A still further object of the present invention is to provide a methodof designing a member pattern which can be planarized completely by theCMP method.

A still further object of the present invention is to suppress anincrease in the parasitic capacitance of an interconnection or the likewhich is caused by the measures to achieve complete planarization,thereby maintaining the performance of the semiconductor integratedcircuit device.

The above-described and other objects, and novel features of the presentinvention will be more apparent from the following description andaccompanying drawings.

Typical features of the invention disclosed by the present applicationwill be described briefly.

(1) The semiconductor integrated circuit device according to the presentinvention comprises actual interconnections which are formed on aprincipal surface of a semiconductor substrate or an interlayerinsulating film constituting a semiconductor integrated circuit element,and an insulating film containing a film which covers the actualinterconnections and has been planarized by the CMP method; whereindummy interconnections, formed of the same material as that of theactual interconnections, but not functioning as an element, are formedin an empty space between adjacent, spaced interconnections in theinterconnection layer where said actual interconnections are formed.

In addition, the semiconductor integrated circuit device according tothe present invention comprises a shallow trench formed on the principalsurface of a semiconductor substrate, an element isolation region havingan insulating film, which contains a film planarized by the CMP method,embedded in the shallow trench, and active regions of the semiconductorintegrated circuit element separated by said element isolation region,wherein dummy regions, which do not function as a semiconductorintegrated circuit element, are formed on the principle surface of thesemiconductor substrate in an empty space of the semiconductor substratebetween said spaced active regions.

By providing such a semiconductor integrated circuit device with dummyinterconnections or dummy regions formed in an empty space to preventthe formation of a sparse portion, the surface of the insulating filmwhich covers the interconnections or the principal surface of thesemiconductor substrate can therefore be planarized completely.

Described more specifically, in the case where only actualinterconnections or active regions (element constituting members) areformed without dummy interconnections or dummy regions (dummy members),an empty space appears between adjacent but spaced element constitutingmembers. If an insulating film is deposited without eliminating such anempty region, the surface of the insulating film near the empty regionbecomes uneven reflecting the shape of each of the element constitutingmembers precisely. Such an uneven shape becomes a factor for inhibitingcomplete planarization, as illustrated in FIG. 29( d).

In accordance with the present invention, therefore, dummy members aredisposed in such an empty region to ease the uneven shape of theinsulating film, whereby the surface of the insulating film isplanarized completely after polishing by the CMP method. The surface ofthe insulating film is planarized completely in this manner so that theprocess margin in the subsequent lithography step or etching step can beincreased. As a result, the production yield of the semiconductorintegrated circuit device can be improved and the starting time for theprocess can be shortened.

Incidentally, examples of the interconnection include a metalinterconnection formed on an interlayer insulating film, a gateinterconnection of a MISFET (Metal-Insulator-Semiconductor Field EffectTransistor) and a bit line of a DRAM (Dynamic Random Access Memory). Itis needless to say that not only the interconnection of memory devices,such as a DRAM, but also the interconnection of logic devices, areincluded in the metal interconnection and gate interconnection. Inparticular, the logic device generally has a multilayer interconnectionformed of at least three layers so that the application of the presentinvention to such an interconnection brings about marked effects.

(2) In another aspect, the semiconductor integrated circuit deviceaccording to the present invention contains a high-density member regionwhich satisfies the conditions that the distance between adjacentmembers of the dummy interconnections and the actual interconnections,or between adjacent members of dummy regions and active regions, is setto at least the minimum space width which is required by the resolutionpower of lithography, and that said distance is set to at least twicethe height of the interconnection or the depth of the shallow trench;and the area of the high-density member region is at least 95% of thewhole chip area.

By setting the distance between the adjacent members of the dummyinterconnections and the actual interconnections or between the adjacentmembers of the dummy regions and active regions at not greater thantwice the height of the interconnections or depth of the shallow trench,there is no pattern dependence of the member pattern on the CMPpolishing rate of the insulating film formed over such members, and theCMP polishing rate becomes uniform, which makes it possible to attainsubstantially complete surface flatness of the insulating film.

FIG. 30 shows data indicating the finding of the present inventorsobtained as a result of test and investigation and it graphicallyrepresents the fluctuation of a CMP polishing amount relative to thedistance between dummy patterns. The distance between dummy patternsstandardized by the height of the pattern is plotted along the abscissa,while the CMP polishing amount of the insulating film on the patternrelative to the standard pattern (solid pattern) is plotted along theordinate. As is apparent from FIG. 30, the CMP polishing amount of theinsulating film does not show a change even it the distance between thedummy patterns becomes approximately twice the height of the pattern. Inother words, if the distance between the adjacent members of the dummyinterconnections and the actual interconnections, or between theadjacent members of the dummy regions and active regions, is set at notgreater than twice the height of the interconnection or the depth of theshallow bench, the CMP rate of the insulating film formed over suchmembers becomes fixed irrespective of the pattern and the insulatingfilm can be planarized completely.

In order to attain planarization over the whole chip, the region wherecomplete planarization can be materialized, that is, the high-densitymember region preferably is as wide as possible, but it is not necessaryfor the whole area of the chip to be a high-density member region. Asufficiently flat surface suited for practical use can be obtained solong as the high-density member region permitting complete planarizationoccupies at least 95% of the chip area.

Another condition that the distance between these members is set at notless than the minimum space width required by the resolution power oflithography is established because a processing space exceeding theminimum processing size is necessary for favorable member processing. Itis possible to carry out processing of the interconnections or dummyinterconnections, or the active regions or dummy regions, by satisfyingthe above condition. Incidentally, when a KrF exima laser is used as anexposure source, 0.2 μm can be given as an example of the minimum spacewidth.

Incidentally, in the remaining 5% region which is not a high-densitymember region, it is preferred that the distance between adjacentmembers of dummy interconnections and actual interconnections, orbetween adjacent members of the dummy regions and active regions, is setat not greater than four times the height of the interconnection or thedepth of the shallow trench. The polishing amount of the insulating filmin such a region where the pattern distance is set at not greater thanfour times the height of the interconnection or the depth of the shallowtrench, that is, a low-density member region shows fluctuations abouttwice as much as that of the high-density member region, as isillustrated in FIG. 30. Because the area of the low-density memberregion is not larger than 5% of the chip area, however, the influence ofthe fluctuation can be neglected.

In addition, in the semiconductor integrated circuit device according tothe present invention, the dummy interconnections or dummy regions eachhave a width not smaller than the minimum line width which is requiredby the resolution power of lithography, or has a length not smaller thantwice the minimum line width; and at the same time, in the scribingarea, the width and length of each of the dummy interconnections ordummy regions is not larger than the distance between bonding pads.Incidentally, the minimum space width and minimum line width can each beset at 0.2 μm and the distance between bonding pads can be set at 10 μm.

According to such a semiconductor integrated circuit device, by settingthe width of each of the dummy interconnections or dummy regions at notsmaller then the minimum line width, which is required by the resolutionpower of lithography, the dummy interconnections or dummy regions can beprocessed with precision; and by setting the length of each of the dummyinterconnections or dummy regions at not less than twice the minimumline width, the resolution of such members can be maintained withcertainty. In other words, there is a potential problem that a patternhaving the minimum processing size in width and length cannot beresolved accurately, but such a potential problem can be avoided in thecase of the present invention by setting the length of each of the dummyinterconnections or dummy regions at not less than twice the minimumprocessing size. The width or length of each of the dummyinterconnections or dummy regions is set at 30 μm or less, with 20 μm orless being frequently used and with 10 μm or less being preferred.

In addition, by setting each of the width and length of the dummyinterconnections or dummy regions at not greater than 30 μm, a parasiticcapacitance of the interconnection and the like and also failure due toshort circuits between the bonding pads can be reduced. Describedspecifically, an increase in the width or length of each of the dummyinterconnections or dummy regions inevitably enlarges such dummymembers, which increases the parasitic capacitance of theinterconnection or the like functioning as a semiconductor integratedcircuit element and impairs the performance of the semiconductorintegrated circuit device, such as the high-speed responsivenessthereof. If the width or length is not greater than 30 μm, on the otherhand, it is possible to suppress the parasitic capacitance of theinterconnection or the like to an extent not causing a problem inpractical use. When the dummy interconnections are disposed in ascribing area, there is a possibility that the scribed chips may becomeconductive dust. Even if they unfortunately become conductive dust, theycause a short-circuit only between bonding pads. So, by setting thewidth and length of each of the dummy interconnections at not greaterthan the distance between the bonding pads, the scribed chips do notcause a short circuit even if they become conductive dust. Owing tothese advantages, deterioration in the performance and yield of thesemiconductor integrated circuit device can be prevented.

In addition, in the semiconductor integrated circuit device according tothe present invention, the dummy interconnections or dummy regions areformed also in the scribing area. According to such a semiconductorintegrated circuit device, complete planarization can be maintained evenin the scribing area, whereby complete planarization all over the wafercan be actualized.

In addition, in the semiconductor integrated circuit device according tothe present invention, a pattern density of interconnections formed ofthe dummy interconnections and actual interconnections, or a patterndensity of regions formed of the dummy regions and active regions, ismade substantially uniform all over the regions on the semiconductorsubstrate.

Even by the semiconductor integrated circuit device as described above,complete planarization of the insulating film on these patterns can beactualized. Described more specifically, as indicated above, theexistence of unevenness in the pattern density inhibits the flatness ofthe insulating film on the pattern. The evenness of the insulating filmis therefore improved also by disposing dummy members so as not to causeunevenness in the pattern density.

(3) In a further aspect, the semiconductor integrated circuit deviceaccording to the present invention is similar to the above-described oneexcept that, in the same interconnection layer which includes a bondingpad portion or marker portion for photolithography disposed on thesemiconductor substrate, dummy interconnections are not formed at theperiphery of the bonding pad portion or a marker portion.

Such a semiconductor integrated circuit device makes it possible tosmoothly perform automatic detection of a bonding pad upon wire bondingand also automatic detection of a marker used for mask alignment duringphotolithography. Described more specifically, if dummy members made ofthe same material as that of the bonding pad or marker have been formedat the periphery thereof, there is a possibility that the dummy memberswill disturb, in the manner of a noise, the smooth detection of thebonding pad or marker. The present invention is free from such apossibility. Incidentally, it is possible that the dummyinterconnections are not formed in a region 20 μm from the bonding padportion or 60 μm from the marker portion.

In addition, the semiconductor integrated circuit device according tothe present invention may contain, as the insulating film, a siliconoxide film formed by the SOG or high-density plasma CVD method, a BPSG(Boron-doped Phospho-Silicate Glass) or PSG (Phospho-Silicate Glass)film formed by the reflow method or a polysilazane film. According tosuch a semiconductor integrated circuit device, since the silicon oxidefilm formed by the SOG or high-density plasma CVD method, the BPSG orPSG film formed by the reflow method or the polysilazane film isexcellent in step covering properties and has properties of embedding aconcave portion therewith, a concave portion formed by adjacent membersof the interconnections and dummy interconnections or of the activeregions and dummy regions is filled in favorably with such a film,whereby the thickness of the insulating film to be polished by the CMPmethod can be decreased. Such a decrease in the thickness of the film tobe polished by the CMP method leads to not only a reduction in the loadof the deposition step of the film to be polished by the CMP method, butalso a reduction in the load of the CMP step, which in turn brings aboutan improvement in the cost competitive advantage of the semiconductorintegrated circuit device, for example, by reducing the process time.

The process for the fabrication of a semiconductor integrated circuitdevice according to the present invention is a process for thefabrication of the above-described semiconductor integrated circuitdevice, which comprises (a) depositing a conductive film containingpolycrystalline silicon or a metal over the principal surface of asemiconductor substrate or over an interlayer insulating film andpatterning said conductive film to form actual interconnections anddummy connections, (b) depositing a first insulating film, which iscomposed of a silicon oxide film formed by the SOG method orhigh-density plasma CVD method, a BPSG or PSG film formed by the re-flowmethod or a polysilazane film, over the actual interconnections anddummy interconnections including inner surfaces of concave portionsformed by the actual interconnections and dummy interconnections andfilling the concave portions with said film, (c) depositing a secondinsulating film over said first insulating film and (d) polishing thesurface of said second insulating film by the CMP method; and whereinthe second insulating film is formed to have a thickness sufficient forplanarizing the unevenness on the surface of the first insulating film.

According to such a fabrication process of a semiconductor integratedcircuit device, the second insulating film can be deposited to give asmaller film thickness, whereby the deposition time of the secondinsulating film can be shortened; and at the same time, the polishingamount of the second insulating film in the CMP polishing step can bereduced. As a result, in spite of the fact that the above processcomprises conventional steps, the step time can be shortened and thestep load can be reduced, which brings about an improvement in the costcompetitive advantage in a semiconductor integrated circuit device.

Described more specifically, in the fabrication process according to thepresent invention, the concave portions formed between the actualinterconnections and dummy interconnections are filled in with the firstinsulating film composed of a silicon oxide film formed by the SOC orhigh-density plasma CVD method, a BPSG or PSG film formed by the re-flowmethod or a polysilazane film, whereby the unevenness remaining on thesurface of the second insulating film is lessened compared with theunevenness before the formation of the film. Accordingly, the thicknessof the second insulating film must be sufficient for the planarizationof the unevenness on the surface of the first insulating film, but thesurface of the second insulating film can be planarized sufficientlyeven by a thin film.

(4) Incidentally, a rigid pad can be used for said CMP polishing.Alternatively, polishing by the CMP method can be employed only for thesurface finish polishing after the unevenness on the surfaceattributable to the existence of the actual interconnections and dummyinterconnections is substantially planarized by the first and secondinsulating films. As a polishing means employed for the surface finish,not only the CMP method, but also other polishing means, such as drybelt polishing and lapping, may be used.

The process for the fabrication of a semiconductor integrated circuitdevice according to the present invention is a process for thefabrication of the above-described semiconductor integrated circuitdevice, which comprises (a) depositing a silicon nitride film on theprincipal surface of a semiconductor substrate and patterning a portionof the silicon nitride film and semiconductor substrate in regionsexcept for the active regions and dummy regions to form a shallowtrench, (b) depositing an insulating film composed of a silicon oxidefilm on the semiconductor substrate, interconnections and siliconnitride film including the inner surface of the shallow trench, therebyfilling in the trench with the insulating film, and (c) polishing theinsulating film by the CMP method to expose the silicon nitride film.

According to the above-described fabrication process of a semiconductorintegrated circuit device, dummy regions are formed also in an elementisolation region so that dishing, that is, the formation of a recess, inthe element isolation region can be prevented and the surface of thesemiconductor substrate can be planarized completely. In addition, sincethe silicon nitride film having a lower CMP polishing rate than thesilicon oxide film is formed between the insulating film, which is afilm to be polished by the CMP method, and the active region of thesemiconductor substrate, the silicon nitride film serves as a stopperlayer for the CMP polishing and more complete flatness can be attained.

Incidentally, the above process may further comprise a step of using analkaline slurry, which contains a silicon oxide as an abrasive, as theslurry used for the CMP method in the step (c) and subsequent to thestep (c), etching of the insulating film formed in the shallow trench isperformed through wet etching or dry etching to make the surface of theinsulating film equal to or lower then the principal surface of thesemiconductor substrate. When the alkaline slurry containing a siliconoxide as an abrasive is used, the ratio of the polishing rate of thesilicon oxide film to the silicon nitride film becomes 3 or 4:1 so thatit is necessary to thicken the silicon nitride film. In such a case,when the height of the principal surface of the semiconductor substrate,that is, the active region, and the height of the silicon oxide film,which is an element isolation region after the removal of the siliconnitride film, are compared, the silicon oxide film is found to behigher. The silicon oxide film is therefore etched by wet etching or dryetching to make the surface of the insulating film equal to or lowerthan the principal surface of the semiconductor substrate, wherebyminute gate processing can be carried out.

Alternatively, a slurry containing cerium oxide as an abrasive can beused as the slurry in the CMP method in the step (c). In this case, theratio of the polishing rate of the silicon oxide film to the siliconnitride film becomes 30 to 50:1 so that it is not necessary to thickenthe silicon nitride film. The thickness of the silicon nitride film canbe set to a value which is negligible in the process, for example, notgreater than 50 nm so that the etching of the silicon oxide filmsubsequent to the removal of the silicon nitride film is not required.

(5) The method of designing a semiconductor integrated circuit deviceaccording to the present invention comprises forming a mask pattern fora mask used for the processing of members each constituting asemiconductor integrated circuit element, wherein said mask patternincludes a member pattern for members and a dummy pattern which is notdisposed in a dummy placement prohibited region; and a mask pattern isformed so as to satisfy all of the following conditions: a firstcondition wherein a pattern distance between adjacent patterns of themember patterns and dummy patterns is not less than the minimum spacewidth which is required by the resolution power of lithography, or notless than 0.2 μm; a second condition wherein the pattern distance is notgreater then twice the height of the member in a region of at least 95%of the chip area, and in a region of at most 5% of the chip area, thepattern distance is not greater than four times the height of themember; a third condition wherein the width of the dummy pattern is atleast the minimum line width which is required by the resolution powerof lithography, or at least 0.2 μm; a fourth condition wherein the widthof the dummy pattern is not greater than the distance between bondingpads disposed in the semiconductor integrated circuit device or notgreater than 10 μm; a fifth condition wherein the length of the dummypattern is not less than twice the minimum line width or not less than0.2 μm; and a sixth condition wherein the length of the dummy pattern isnot greater than the distance between the bonding pads or not less than10 μm.

Such a method of designing a semiconductor integrated circuit devicemakes it possible to design a mask for member patterns necessary for thefabrication of said semiconductor integrated circuit device. By theabove-described conditions, the advantages of the above-describedsemiconductor integrated circuit device can be actualized.

Incidentally, it is needless to say that the dummy pasterns can bedisposed also in a scribing area of the semiconductor substrate. Thedummy placement prohibited-region can be set within a range of 20 μmfrom an end portion of the pattern to be a bonding pad, a range of 60 μmfrom an end portion of the pattern to be a marker for photolithography,a range of 0.5 μm from a region in which a contact hole is to be formed,or a fuse region. By setting the dummy placement prohibited region asdescribed above, it becomes easier to detect the bonding pad or themarker for the mask alignment upon wire bonding or photolithography,which makes it possible to form a contact hole between theinterconnections of different layers or a contact hole between theinterconnection and the semiconductor substrate.

In the case of a metal interconnection wherein the member and thestorage capacitative element which is to be formed above a bit line areformed in substantially the same layer, the dummy placement can beprohibited in a region which is to have a storage capacitative elementthereon. In such a case, the first metal interconnection layer and thestorage capacitative element of a DRAM can be formed in the same layerand dummy interconnections can be disposed in a region of the firstmetal interconnection layer.

In the case of the active region wherein members are formed on theprincipal surface of the semiconductor substrate, the placement of dummyregions can be prohibited in a region wherein a gate interconnection isformed on the principal surface of the semiconductor substrate. In sucha case, since no dummy region is formed belong the gate interconnection,the capacitance between the gate interconnection and the semiconductorsubstrate can be reduced. Described more specifically, because the dummyregions on the principal surface of the semiconductor substrate and theactive region of the semiconductor substrate apparently have the samestructure, the formation of the gate interconnection on the dummyregions increases the capacitance of the gate interconnection. The dummyregions are therefore not formed below the gate interconnection, whichbrings about an improvement in the performance of the semiconductorintegrated circuit device, such as the high-peed responsiveness thereof.

In addition, the method of designing a semiconductor integrated circuitdevice according to the present invention comprises disposing dummypatterns so as to minimize the floating capacitance of a member whichwill otherwise be increased by the dummy members formed by the dummypatterns, whereby the performance of the semiconductor integratedcircuit device, such as the high-speed responsiveness thereof, can beimproved. Incidentally, such disposal of elements can be effected bysatisfying the above-described conditions for the method of designing asemiconductor integrated circuit device and then, optimizing the dummypatterns so as to minimize the area and the number of the dummypatterns. Such optimization can be calculated automatically by aninformation processor such as computer which forms a layout pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating one example of a logicintegrated circuit device according to Embodiment 1 of the semiconductorintegrated circuit device of the present invention;

FIG. 2 is a fragmentary plan view illustrating the layout of theinterconnections and dummy interconnections in the first interconnectionlayer in FIG. 1;

FIG. 3( b) is a plan view illustrating a layout rule applied to thelayout of the interconnections and dummy interconnections and FIG. 3( a)is a cross-sectional view taken along a line A—A of FIG. 3(-b);

FIG. 4 is a cross-sectional view illustrating an enlargedinterconnection portion in FIG. 1;

FIG. 5 is a cross-sectional view illustrating one example of thefabrication process of the logic integrated circuit device according toEmbodiment 1 in the order of the steps;

FIG. 6 is a cross-sectional view illustrating one example of thefabrication process of the logic integrated circuit device according toEmbodiment 1 in the order of the steps;

FIG. 7 is a cross-sectional view illustrating one example of thefabrication process of the logic integrated circuit device according toEmbodiment 1 in the order of the steps;

FIG. 8 is a cross-sectional view illustrating one example of thefabrication process of the logic integrated circuit device according toEmbodiment 1 in the order of the steps;

FIG. 9 is a cross-sectional view illustrating one example of thefabrication process of the logic integrated circuit device according toEmbodiment 1 in the order of the steps;

FIG. 10 is a cross-sectional view illustrating one example of thefabrication process of the logic integrated circuit device according toEmbodiment 1 in the order of the steps;

FIG. 11 is a cross-sectional view illustrating one example of thefabrication process of the logic integrated circuit device according toEmbodiment 1 in the order of the steps;

FIG. 12 is a cross-sectional view illustrating one example of a logicintegrated circuit device according to Embodiment 2;

FIG. 13 is a plan view illustrating a layout of interconnections anddummy interconnections in the fifth interconnection layer;

FIG. 14 is a cross-sectional view illustrating one example of a logicintegrated circuit device according to Embodiment 3 of the presentinvention;

FIGS. 15( a) and (b) are each a plan view illustrating another exampleof the logic integrated circuit device according to Embodiment 3;

FIG. 16 is a cross-sectional view illustrating one example of DRAMaccording to Embodiment 3;

FIG. 17 is a graph illustrating a relationship between a pattern sizeand focus depth of lithography;

FIG. 18 is a cross-sectional view illustrating one example of thefabrication process of DRAM according to Embodiment 3 in the order ofthe steps;

FIG. 19 is a cross-sectional view illustrating one example of thefabrication process of DRAM according to Embodiment 3 in the order ofthe steps;

FIG. 20 is a cross-sectional view illustrating one example of thefabrication process of DRAM according to Embodiment 3 in the order ofthe steps;

FIG. 21 is a cross-sectional view illustrating one example of thefabrication process of DRAM according to Embodiment 3 in the order ofthe steps;

FIG. 22 is a cross-sectional view illustrating one example of afabrication process of DRAM according to Embodiment 3 in the order ofthe steps;

FIG. 23 is a cross-sectional view illustrating one example of asemiconductor integrated circuit device according to Embodiment 4;

FIG. 24 is a plan view illustrating one example of the semiconductorintegrated circuit device according to Embodiment 4;

FIG. 25 is a cross-sectional view illustrating one example of thesemiconductor integrated circuit device according to Embodiment 4 in theorder of the steps;

FIG. 26 is a cross-sectional view illustrating one example of thesemiconductor integrated circuit device according to Embodiment 4 in theorder of the steps;

FIG. 27 is a cross-sectional view illustrating one example of thesemiconductor integrated circuit device according to Embodiment 4 in theorder of the steps;

FIG. 28 is a cross-sectional view illustrating one example of thesemiconductor integrated circuit-device according to Embodiment 4 in theorder of the steps;

FIGS. 29( a) to 29(d) are each a cross-sectional view illustratingplanarization technique by the CMP method investigated by the presentinventors;

FIG. 30 is a graph illustrating the fluctuations of CMP polishing amountrelative to the distance between patterns;

FIG. 31 is a plan view illustrating one example of the semiconductorintegrated circuit device according to Embodiment 4 of the presentinvention;

FIG. 32 is a cross-sectional view illustrating one example of asemiconductor integrated circuit device according to Embodiment 5 of thepresent invention;

FIG. 33 is a fragmentary plan view of the semiconductor integratedcircuit device of FIG. 32; and

FIG. 34 is a fragmentary plan view of the semiconductor integratedcircuit device of FIG. 32

EMBODIMENTS OF THE PRESENT INVENTION

The embodiments of the present invention will next be described indetail with reference to accompanying drawings. Incidentally, in each ofthe drawings illustrating the following embodiments, like elements willbe identified by like reference numerals and overlapping descriptionswill be omitted.

(Embodiment 1)

FIG. 1 is a cross-sectional view illustrating one example of a logicintegrated circuit device according to Embodiment 1 of the semiconductorintegrated circuit device of the present invention. In FIG. 1, ascribing area A, a pad and peripheral circuit region B and a logiccircuit region C of the semiconductor integrated circuit device areillustrated.

In the logic integrated circuit device according to Embodiment 1, ashallow trench 2 is formed on the principal surface of the semiconductorsubstrate 1, and in the shallow trench 2 a silicon oxide film, which isan insulating film, is embedded, whereby an element isolation region 3is formed. By this element isolation region 3, an active region 4 formedon the principal surface of the semiconductor substrate 1 is defined.Incidentally, as an element isolation structure, a shallow trench isexemplified here, but a field insulating film formed by the LOCOS (LocalOxidation of Silicon) method may be employed as well. Although notillustrated here, P-type and N-type well regions may be formed on theprincipal surface of the semiconductor substrate.

In the active region 4, a MISFET is formed. On the principal surfaceof—the semiconductor substrate, a gate interconnection 6 is formed via agate insulating film 5 of the MISFET. The gate insulating film 5 maybe,for example, a silicon oxide film formed by thermal oxidation, while thegate interconnection 6 may be, for example, a polycrystalline siliconfilm formed by the CVD method. On the surface of the polycrystallinesilicon film, a silicide film is formed in order to reducethe—electrical resistance.

A portion of the gate interconnection 6 is formed to extend over theelement separation region 3 and another portion is formed to be a gateelectrode 7 of a MISFETQ1 formed in the active region 4 of thesemiconductor substrate 1. On both sides of the gate electrode 7 in theactive regions 4 on the principal surface of the semiconductor substrate1, impurity semiconductor regions 8 are formed. The impuritysemiconductor regions 8 function as a source drain region for theMISFETQ1. It is also possible to employ the region 8 as a so-called LDD(Lightly Doped Drain). On the side of the gate interconnection 6, a sidewall spacer 8 b is formed. The side wall spacer 8 b can be formed of asilicon oxide film or a silicon nitride film.

The MISFETQ1 formed in the logic circuit region C functions as an activedevice for the logic circuit. Although not illustrated in FIG. 1, theMISFET formed in the pad and peripheral circuit region B functions as anactive device for the peripheral circuit. Incidentally, the MISFET isexemplified as a transistor formed in the logic circuit region C and padand peripheral circuit region B, but a bipolar transistor or Bi-CMOStransistor can also be employed.

The gate interconnection 6 is covered with an interlayer insulating film9, over which interconnections 10 and dummy interconnections 11 areformed in the first interconnection layer. The interlayer insulatingfilm 9 can be formed, for example, of a PSG film, BPSG film or a siliconoxide film such as SOG film. Alternatively, a lamination film with aTEOS silicon oxide film can be used for the prevention of diffusionof—impurities. It is preferred that the surface of the interlayerinsulating film 9 has been planarized by the CMP method or etchbackmethod.

The interconnection 10 and dummy interconnection 11 are made of the samematerial and formed by the same step (same layer). Examples of thematerial include metals, such as aluminum (Al) and copper (Cu). They mayalternatively be made of a polycrystalline silicon film doped withimpurities at a high concentration. In the case of the polycrystallinesilicon film, the surface thereof may be converted into a silicide.

FIG. 2 is a plan view illustrating the layout of the interconnections 10and dummy interconnections 11 in the first layer. The dummyinterconnections 11 are formed in a region (void region) where the spacebetween adjacent interconnections 10 is wide. As a result, the dummyinterconnections are placed evenly in a region where theinterconnections 10 have not been disposed, the space between theadjacent members of the dummy interconnections 11 and interconnections10 becomes narrow; and the dummy interconnections seem to be filled inthe void region densely.

The dummy interconnections 11 are formed also in the scribing area A,whereby the flatness of an insulating film 12 is maintained all over thesemiconductor substrate 1, which will be described later. The width andlength of the dummy interconnection 11 formed in the scribing area A areconstituted so as to be not greater than the distance between thebonding pads.

FIG. 3( b) is a plan view illustrating a layout rule applied to theplacement of the interconnections 10 and the dummy interconnections 11,and FIG. 3( a) is a cross-sectional view taken along a line A—A of FIG.3( b).

The member space S, which is a space between the interconnection 10 andthe dummy interconnection 11, or a space between adjacent dummyinterconnections 11, is not greater than twice the height of theinterconnection height H of the dummy interconnection 11 orinterconnection 10. As described above with reference to FIG. 30, bysetting the member space S at not greater than twice the interconnectionheight H, the CMP polishing amount of the insulating film 12 can be madeuniform and the surface of the insulating film 12 can be completelyplanarized. In a region not wider than 5% of the chip area, the memberspace S is allowed to have a height of at most four times theinterconnection height H. In this case, although the fluctuations of thepolishing amount of the insulating film 12 increase about twice, theycan be neglected as a whole because this area amounts to not greaterthan 5% of the chip area. The flatness of the whole insulating film 12therefore can be substantially maintained.

In addition, as the member space S, a space not smaller than the minimumspace width required by a lithographic tool is necessary. This conditionpermits accurate processing of the interconnection 10 and dummyinterconnection 11, whereby each member can be processed accuratelyaccording to the design. In the case of an exposure apparatus using aKRF exima laser as a light source, 0.2 μm can be given as an example ofthe minimum space width.

The width (a) of the dummy interconnection 11 is set to be not smallerthan the minimum line width required by a lithographic tool. By settingthe width (a) to be not smaller than the minimum line width, the dummyinterconnections 11 can be processed with certainty. In the scribingarea, the width (a) of each of the dummy interconnections 11 is set atnot greater than the distance between bonding pads 13. By doing so, evenif the dummy interconnections 11 are peeled off into minute chips bydicing or the like and produce conductive dust, no short circuit occursbetween the bonding pads 13, which makes it possible to eliminate acause for possible failure. The width (a) of each of the dummyinterconnections 11 is set to be, for example, not greater than 30 μm,with 20 μm being frequently employed and with 10 μm being preferred. Thedistance between the bonding pads 13 can be set at about 10 μm. Even ifthe dummy interconnections 11 of such a size are formed, the parasiticcapacitance of the interconnection 10 does not increase and thereforedoes not cause a problem of retarding a signal transferred to theinterconnection 10. As a result, the performance of the logic integratedcircuit device is not deteriorated.

The length (b) of each of the dummy interconnections 11 is set at notless than twice the minimum line width, and in the scribing area, it isset at not greater than the distance between the bonding pads, forexample, not greater than 10 μm. When the width (b) and length (a) ofeach of the dummy interconnections 11 are each set at the minimum linewidth, there is a possibility that proper resolution of the dummyinterconnections 11 will not be attained. By setting the length (b) atleast twice the minimum line width, the resolution of the dummyinterconnections 11 can be carried out with certainty even if the width(a) is the minimum line width, which makes it possible to process itwith certainty. For the same reason in the width (a), the length (b) isset at, for example, not greater than the distance between bonding pads,for example, not greater than 10 μm. Similar to the width (a), thelength (b) of each of the dummy interconnections 11 is constituted atnot greater than 30 μm, with 20 μm or less being frequently employed andwith 10 μm or less being preferred.

In Embodiment 1, the dummy interconnections 11 are in a rectangularform, but may be in a triangular, trapezoidal, circular or anotherpolygonal form so long as they satisfy the above-described conditions.For minimizing the parasitic capacitance of the interconnection 10, thesize and number of the dummy interconnections 11 are each preferred tobe as small as possible. For minimizing the parasitic capacitance of theinterconnection 10 within a range satisfying the above-describedconditions, it is most preferred to set the member space S at twice theinterconnection height H, the width (a) of each of the dummyinterconnections at the minimum line width and the length (b) of each ofthe dummy interconnections at not less than twice the minimum linewidth. In this Embodiment, for example, the dummy interconnections areconstituted to have a width (a) of 0.6 to 1 μm and a length (b) of 10 to25 μm.

The interconnections 10 and dummy interconnections 11 are covered withthe insulating film 12. The surface of the insulating film 12 has beenpolished by the CMP method so that the film has a completely planarizedsurface.

FIG. 4 is an enlarged cross-sectional view of the interconnectionportion of FIG. 1. The insulating film 12 has an insulating film 12 a,an insulating film 12 b, an insulating film 12 c and an insulating film12 d laminated in this order from the side contiguous to theinterconnection 10 and dummy interconnection 11.

As the insulating film 12 a, a silicon oxide film formed by the CVDmethod using TEOS can be employed for example. As illustrated in thedrawing, the insulating film 12 a is formed, faithfully tracing thesurface line including a step difference. The film thickness can be set,for example, at 300 nm.

As the insulating film 12 b, an inorganic SOG film, a silicon oxide filmformed by the high-density plasma CVD method or a polysilazane film canbe employed. In short, a film having properties for filling a concaveportion therewith can be employed. As illustrated in the drawing, thefilm is embedded in the concave portion and the thickness of the film inthe convex portion is formed to be thin. The reason why the concaveportion can be embedded with the insulating film 12 b is because theabove-described dummy interconnections 11 are formed under theabove-described conditions and the concave portion formed betweenadjacent dummy interconnections 11 is not greater than a given spacenecessary for embedding the insulating film 12 b. The film thickness isfor example set at 125 nm on the convex portion.

As the insulating film 12 c, for example, a silicon oxide film formed bythe CVD method using TEOS can be employed, with its surface beingpolished by the CMP method. The existence of the dummy interconnections11 has enabled complete planarization of the polished surface. This filmcan be formed to give a thickness of 500 nm on the convex portion.

As the insulating film 12 d, a silicon oxide film formed by the CVDmethod using TEOS can be employed. It has, for example, a film thicknessof 200 nm. Incidentally, the insulating film 12 d can be omitted. Insuch a case, it is necessary to add the thickness of the insulating film12 d to the thickness of the insulating film 12 c upon deposition of theinsulating film 12 c.

Over the insulating film 12, interconnections 14, dummy interconnections15 and an insulating film 16 of the second interconnection layer areformed, over which interconnections 17, dummy interconnections 18 and aninsulating film 19 of the third interconnection layer are formed andthen, interconnections 20, dummy interconnections 21 and an insulatingfilm 22 are formed. The interconnections 14, 17 and 20, dummyinterconnections 15, 18 and 21 and insulating films 16, 19 and 22 areformed similarly to the interconnection 10, dummy interconnection 11 andinsulating film 12 of the first interconnection layer, respectively.

Over the fourth interconnection layer, interconnections 23 and aninsulating film 24 of the fifth interconnection layer are formedfollowed by the formation of a passivation film 25. As the passivationfilm 25, for example, a silicon nitride film can be employed. Theinterconnections 23 include the bonding pad 13.

A process for the fabrication of the logic integrated circuit device ofEmbodiment 1 will next be described with reference to FIGS. 5 to 11,which are cross-sectional views illustrating one example of thefabrication process of the logic integrated circuit device of Embodiment1 in the order of the steps thereof.

As illustrated in FIG. 5, on a semiconductor substrate 1, a shallowtrench 2 is formed using photolithography and etching techniques. On theprincipal surface of the semiconductor substrate 1 having the shallowtrench 2 formed therein, a silicon oxide film is deposited, and then, itis polished by the CMP method or the like to form an element isolationregion 3. Then, N-type and P-type well regions may be formed.

As illustrated in FIG. 6, a silicon oxide film to be a gate insulatingfilm 5 is then formed by the thermal oxidation or thermal CVD method,followed by the deposition of a polycrystalline silicon film by the CVDmethod. The polycrystalline silicon film is patterned usingphotolithography and etching techniques, whereby a gate interconnection6 (gate electrode 7) is formed. With the gate electrode 7 serving as amask, impurities are subjected to ion implantation in self alignmentrelative to the gate electrode 7, whereby an impurity semiconductorregion 8 is formed. After the deposition of a silicon oxide film,anisotropic etching is conducted, whereby a side-wall spacer 8 b isformed. It is possible to carry out ion implantation ofhighly-concentrated impurities to form the impurity semiconductor region8 as a so-called LDD structure.

As illustrated in FIG. 7, a PSG film is formed, followed byplanarization by the etchback or CMP method, whereby an interlayerinsulating film 9 is formed. Over the interlayer insulating film, analuminum film is deposited by the sputtering or deposition method. Thealuminum film so obtained is patterned by photolithography and etchingtechniques, whereby interconnections 10 and dummy interconnections 11are formed. Patterning is conducted in accordance with the conditions asdescribed above with regards to the dummy interconnections 11.

As illustrated in FIG. 8, an insulating film 12 a is formed by the CVDmethod using TEOS. As the CVD method, a plasma CVD method can beemployed, but a thermal CVD method using ozone in combination can beemployed alternatively. The film thickness of the insulating film 12 ais set at 300 nm. Incidentally, FIGS. 8 to 11 are cross-sectional viewseach illustrating only an interconnection layer and the layerstherebelow are omitted.

Then, an insulating film 12 b is formed using an inorganic SOG film andgaps formed by adjacent ones of the interconnections 10 and dummyinterconnections 11 are filled therewith. The inorganic SOG film can beformed by coating inorganic SOG and then baking it. The film thicknessof the insulating film 12 b is set at 125 nm on the convex portion.Incidentally, the insulating film 12 b may be a silicon oxide filmformed by the high-density plasma CVD method or a polysilazane film.

Since the width of the gap is narrow owing to the formation of the dummyinterconnections 11, it becomes possible to embed the gap with theinsulating film 12 b favorably. In other words, the film thickness inthe concave portion is made thicker than that on the convex portion. Asa result, the unevenness on the surface of the insulating film 12 b islessened and the difference in the height can be reduced.

As illustrated in FIG. 9, an insulating film 12 c is then formed by theCVD method using TEOS. The insulating film 12 can be formed to have afilm thickness of 700 nm. In the case where no dummy interconnection isdisposed as is illustrated in FIG. 29, the thickness of the insulatingfilm 12 c is required to be about 1700 nm, but in Embodiment 1, thethickness can be decreased to 700 nm because of the presence of thedummy interconnections 11. As a result, the step for deposition theinsulating film 12 can be shortened, whereby the step load can bereduced.

As illustrated in FIG. 10, the surface of the insulating film 12 c isthen polished by the CMP method and planarized. In Embodiment 1, thesurface shape of the insulating film 12 c reflects the shapes of theinterconnections 10 and dummy interconnections 11, as well as that ofthe insulating film 12 b, so that the insulating film 12 c hassubstantially an even height at any place. As a result, the polishingrate becomes substantially uniform irrespective of the locations,whereby the surface of the insulating film 12 c can be substantiallyplanarized. In addition, the insulating film 12 c has a film thicknessas little as 700 nm, which makes it possible to reduce the CMP polishingamount and to reduce the load of the CMP polishing step. Incidentally,the polishing amount can be decreased to 200 nm.

Then, a surface washing after CMP polishing is effected, followed by theformation of an insulating film 12 d by the CVD method-using TEOS, as isillustrated in FIG. 11. The insulating film 12 d can be formed to have athickness of 200 nm. Incidentally, it is possible to omit the insulatingfilm 12 d and to form the insulating film 12 c to have a thickness of900 nm.

In this manner, the first interconnection layer is completed. Similar tothe first interconnection layer, the second to fourth interconnectionlayers are then formed, followed by the formation of the fifthinterconnection layer similarly. Over the fifth interconnection layer, apassivation film 25 is formed, whereby the logic integrated circuitdevice as illustrated in FIG. 1 is almost completed.

According to the fabrication process of Embodiment 1, the surfaces ofthe insulating films 12, 16, 19 and 22 are completely planarized and atthe same time, the step for deposition of an insulating film to bepolished by CMP and CMP polishing step can be shortened, whereby steploads can be reduced. In general, such an advantage becomes particularlymarked when a multi-layer interconnection, such as a logic device,composed of at least 3 layers is formed.

Incidentally, an interconnection layer composed of five layers isexemplified in this Embodiment 1, however, it may be formed of anynumber of layers either greater or less than five layers.

(Embodiment 2)

FIG. 12 is a cross-sectional view illustrating one example of a logicintegrated circuit device according to Embodiment 2 of the presentinvention.

The logic integrated circuit device according to Embodiment 2 issubstantially similar to that of Embodiment 1 except for the fifthinterconnection layer. Accordingly, description of the common featuresis omitted herein and only the differences will be described below.

The logic integrated circuit device according to Embodiment 2 has, inthe fifth interconnection layer, dummy interconnections 26 in additionto interconnections 23. The dummy interconnections 26 are disposed undersubstantially similar conditions to the dummy interconnections 11described in Embodiment 1. The interconnections 23 of the fifthinterconnection layer however include the bonding pad 13 so that thedisposing conditions of the dummy interconnections 26 are different atthe periphery of the bonding pad 13.

FIG. 13 is a plan view illustrating the layout of the interconnections23 and the dummy interconnections 26 of the fifth interconnection layer.At the periphery of the bonding pad 13, a prohibited area 27 free fromdummy interconnections 26 is disposed. The prohibited area 27 can extendwithin a range of 20 μm from each end of the bonding pad 13.

Such a logic integrated circuit device makes it possible to completelyplanarize also the surface of the passivation film 25, because the dummyinterconnections 26 are formed in the fifth interconnection layer. As aresult, it becomes possible to carry out processing of a BLM (BallLimiting Metalization) film 29, which is to be an underground film for abump 28, as illustrated in FIG. 14. In addition, by disposing theprohibited area 27 at the periphery of the bonding pad 13, automaticdetection of the bonding pad 13 by a wire bonding apparatus can beconducted with certainty.

Incidentally, in the present Embodiment 2 and also the above-describedEmbodiment 1, the dummy interconnections 11, 15, 18, 21 and 26 can beformed in the scribing area A. When markers 30 a and 30 b forlithography are formed, as illustrated in FIGS. 15( a) and 15(b),respectively, in the scribing area A or another area, prohibited areas31 a and 31 b free from the placement of the dummy interconnections 11,15, 18, 21 or 26 can be disposed in the vicinity of the markers. Theprohibited area 31 a or 31 b can be disposed within a range of 60 μmfrom each end of the marker 30 a or 30 b.

By disposing such a prohibited area 31 a or 31 b, it becomes possible tocarry out automatic detection of the marker 30 a or 30 b favorably by anexposure apparatus used for photolithography. Incidentally, theprohibited area 31 a or 31 b is formed for at least the dummyinterconnections 26 of the uppermost interconnection layer, and it isnot necessary to apply it to the dummy interconnections 11, 15 and 18 inthe lower interconnection layers. Alternatively, it is not necessary todispose the-dummy interconnections themselves.

(Embodiment 3)

FIG. 16 is a cross-sectional view illustrating one example of a DRAMwhich represents Embodiment 3 of the present invention.

A semiconductor substrate 1, a shallow trench 2, an element isolationregion 3 and an active region 4 of DRAM according to Embodiment 3 aresimilar to those of Embodiment 1. On the principal surface of thesemiconductor substrate 1, a p-type well region 32 and an n-type wellregion 33 are formed.

In the active region 4 of the p-type well region 32, a selectiveMISFETQt constituting a memory cell M of the DRAM and a MISFETQn of aperipheral circuit are formed, while in the active region 4 of then-type well region 33, MISFETQp of the peripheral circuit is formed. InFIG. 16, shown on the left side is a memory cell area, while on thecenter and right side, a peripheral circuit area is shown. The memorycell M of the DRAM has a selective MISFETQt and a storage element SNwhich is a capacitative element.

Gate electrodes 7 for MISFETQt, MISFETQn and MISFETQp are each formed ofa polycrystalline silicon film, said film having a suicide layer 7 a onthe surface thereof. In the active region 4 existing on both sides ofthe gate electrode 7 for MISFETQt, MISFETQn or MISFETQp, impuritysemiconductor regions 8 are formed and constitute a source and drainregion of the MISFET. The conductivity type of the impuritysemiconductor region 8 differs depending on the conductivity type of theMISFET. The MISFETQt and the MISFETQn have an n-type conductivity, whilethe MISFETQp has a p-type conductivity. Incidentally, concerning theMISFETQn and MISFETQp of the peripheral circuit, the impuritysemiconductor regions 8 are illustrated to have an LDD structure, but itis not necessary that they have an LDD structure.

In the layer where the gate electrodes 7 exist, gate interconnections 6and dummy gate interconnections (dummy members) 34 are formed. The gateelectrodes 7 are also part of the gate interconnections 6. Since thegate interconnections 6 and dummy gate interconnections 34 are formedsimultaneously with the gate electrodes 7 (in the same layer), silicidelayers 6 a and 34 a are formed on the surfaces thereof. On the sidewalls and upper surfaces of the gate interconnections 6 and dummy gateinterconnections 34, side walls 8 b and cap insulating films 8 c, eachformed of a silicon oxide film, are formed, over which an insulatingfilm 35 is formed. The insulating film 35 may be formed of, for example,a TEOS silicon oxide film. Over the insulating film 35, an insulatingfilm 36 planarized by the CMP method is formed. The insulating film 36may be formed, for example, of a BPSG film. In Embodiment 3, dummy gateinterconnections 34 are disposed so that the insulating film 36 can bealmost completely planarized. Even if the focus depth of the lithographybecomes shallow, such complete planarization makes it possible to mass-produce the products, on which minute patterns on the level of 0.2 μmhave been formed, as illustrated by FIG. 17.

The dummy gate interconnections 34 are disposed under similar conditionsto those for the dummy interconnections 11 described in Embodiment 1.Incidentally, the dummy gate interconnections 34 are not disposed in aregion where a contact hole is to be formed, which makes it possible toopen the contact hole smoothly. The dummy gate interconnections 34 areformed mainly on the element isolation region 3.

Over the insulating film 36, an insulating film 37 composed of, forexample, a silicon oxide film formed using TEOS can be formed.Alternatively, it can be omitted. Over the insulting film 37, inaddition to the bit line 38 of the DRAM, interconnections 39 and dummyinterconnections 40, which are formed in the same layer with the bitline, are formed. These interconnections can be composed of apolycrystalline silicon film having, for example, a CVD tungsten film asan adhesive layer. The dummy interconnections 40 are formed inaccordance with the conditions employed for the above-described dummyinterconnections 11 of Embodiment 1. However, they are not disposed in aregion having a contact hole formed therein, whereby the contact holecan be opened smoothly. On the side walls and upper surfaces of the bitline 38, interconnection 39 and dummy interconnection 40, side walls 41b and cap insulating film 41 c, each composed of a silicon oxide film,are formed, over which an insulating film 42 is laid. The insulatingfilm 42 is composed of, for example, a BPSG film which has been polishedby the CMP method for planarization. Incidentally, an insulating film 43composed of a silicon oxide film formed using TEOS can be formed overthe insulating film 42, but alternatively, it can be omitted. In thisEmbodiment 3, the dummy interconnections 40 are disposed, which makes itpossible to planarize the insulating film 42 almost completely.

Over the insulating film 43, a storage capacitative element SN of theDRAM and a first metal interconnection layer are formed. The storagecapacitative element SN is constituted of a lower electrode 45 which isconnected with the impurity semiconductor region 8 of a MISFETQt througha plug 44, and a plate electrode 47 formed opposite to the lowerelectrode 45 through a capacitative insulating film 46. The storagecapacitative element SN is covered with an insulating film 48. It isalso covered with an insulating film 49 composed of a silicon oxide filmformed, for example, by the high-density plasma method. Over theinsulating film 49, the interconnections so and dummy interconnections51 of the first interconnection layer are formed. Each of theinterconnections so is connected through the contact hole with a plateelectrode 47 or an impurity semiconductor region 8 on the principalsurface of the semiconductor substrate 1. The interconnections so anddummy interconnections 51 are formed simultaneously, and they arecomposed of, for example, a tungsten film having as an adhesive layerCVD tungsten or an aluminum film. The dummy interconnections 51 aredisposed under similar conditions to those described in Embodiment 1with regard to the dummy interconnections 11. However, they are notdisposed in a memory mat region in which the storage capacitativeelement SN is to be formed.

The interconnections 50 and dummy interconnections 51 are covered withan insulating film 52 composed of, for example, a silicon oxide filmformed by the high-density plasma CVD method or a polysilazane film.Over the insulating film 52, an insulating film 53 composed of a TEOSsilicon oxide film is formed. The insulating film 53 is polished by theCMP method and planarized. It has almost complete flatness because ofhaving therebelow the dummy interconnections 51. The insulating film 53is overlaid with interconnections 54, dummy interconnections 54 and aninsulating film 56 of the second layer, followed by the formation of theinterconnections 57, dummy interconnections 58 and an insulating film 59of the third layer. The interconnections 54, dummy interconnections 55,insulating film 56, interconnections 57, dummy interconnections 58 andinsulating film 59 are formed in a similar manner to theinterconnections 10, dummy interconnections ii and insulating film 12 inEmbodiment 1.

The DRAM according to Embodiment 3 makes it possible to provide eachinsulating film with complete flatness because dummy members 34, 40, 51,55 and 58 are disposed for the gate interconnections 6, bit line 38,interconnections so of the first layer, interconnections 54 of thesecond layer and interconnections 57 of the third layer. By disposingthe dummy gate interconnections 34 and dummy interconnections 40, 51, 55and 58 between the memory cell region and peripheral circuit area, theinsulating film of each layer can be planarized.

Incidentally, the process for the fabrication of the DRAM of Embodiment3 will next be described with reference to FIGS. 18 to 21. FIGS. 18 to21 are cross-sectional views each illustrating one example of thefabrication process of the DRAM of Embodiment 3 in the order of thesteps thereof.

The steps leading up to the formation of the element isolation region 3on the principal surface of the semiconductor substrate 1 are similar tothose of Embodiment 1 so that their description will be omitted.

Then, as illustrated in FIG. 18, a silicon oxide film, which will be agate insulating film 5, is formed, followed by the deposition thereon ofa polycrystalline silicon film to be a gate interconnection 6, gateelectrode 7 and dummy gate interconnection 34, and then a silicon oxidefilm which will be formed as a cap insulating film 8 c. These films solaminated are patterned, whereby the gate interconnection 6, gateelectrode 7 and dummy gate interconnection 34 are formed. The gateinterconnection 6 (gate electrode 7) is patterned in accordance with anordinarily employed layout rule, while the dummy gate interconnection 34is patterned so as to be disposed in the element isolation region 3,while substantially satisfying, in addition to the ordinarily employedlayout rule, the conditions in Embodiment 1 concerning the dummyinterconnection 11.

Then, as illustrated in FIG. 19, a side-wall spacer 8 b is formed,followed by the deposition of an insulating film 35 and then a BPSGfilm. The BPSG film is thereafter polished by the CMP method, whereby aninsulating film 36 is formed. The BPSG film can be formed to give athickness of 800 nm and the CMP polishing amount can be suppressed to400 nm. When the dummy gate interconnections 34 are not formed, it isnecessary to deposit a thicker BPSG film and the CMP polishing amountinevitably increases. As described above, by decreasing the thickness ofthe BPSG film and reducing the CMP polishing amount, advantages such asreduction in the step load can be brought about. Incidentally, insteadof the BPSG film, a PSG film or a silicon oxide film formed by thehigh-density plasma CVD method can be employed. Also, the side wallspacer 8 b and the cap insulating film 8 c can each be formed of asilicon nitride film, instead. When the silicon nitride film is used,etching upon the opening of a contact hole can be carried out by selfalignment.

As illustrated in FIG. 20, subsequent to the washing after the CMPpolishing, an insulating film 37 is deposited to a thickness of 100 nm.It is also possible to omit the insulating film 37. Then, a plug 44 tobe connected with a bit line 38 and a lower electrode 45 of a storagecapacitative element SN are formed, followed by the formation of the bitline 38, interconnections 39 and dummy interconnections 40. The dummyinterconnections 40 are disposed under similar conditions to those forthe dummy interconnections 11 of Embodiment 1. Then, a side wall 41 band a cap insulating film 41 c are formed and a BPSG film is depositedthereon, followed by polishing of the BPSG film by the CMP method,whereby an insulating film 42 is formed. Incidentally, instead of theBPSG film, a PSG film or a silicon oxide film formed by the high-densityplasma CVD method can be employed. Since the dummy interconnections 40have been formed, the insulating film 42 is able to have a completelyplanarized surface and at the same time, it is possible to decrease thethickness of the BPSG film and reduce the CMP polishing amount. Then,washing is effected after the CMP polishing, followed by the depositionof an insulating film 43 by the plasma CVD method using TEOS or the likemethod. It is also possible to omit this insulating film 43.

Then, as illustrated in FIG. 21, a storage capacitive element SN isformed and a BPSG film is deposited thereon, followed by a bakingtreatment, whereby an insulating film 49 is formed. The insulating film49 can be formed to a thickness of 500 nm. Subsequent to the opening ofa contact hole, a tungsten film to be a first interconnection layer isformed by the CVD method, followed by the formation of an aluminum filmby the sputtering method. Then, the resulting aluminum and tungstenfilms are patterned, whereby interconnections 50 and dummyinterconnections 51 are formed. The dummy interconnections 51 aredisposed under similar conditions to those for the dummyinterconnections 11, and in addition, it is a condition that the dummyinterconnections 51 are not disposed in a memory mat region where thestorage capacitative device is disposed. FIG. 22 is a plan viewillustrating the above conditions. A BPSG film is then deposited to forman insulating film 52. A TEOS silicon oxide film is deposited thereover,followed by polishing by the CMP method, whereby an insulating film 53is formed. Instead of the BPSG film, a PSG film or a silicon oxide filmformed by the high-density plasma CVD method can be employed. Here, theformation of the dummy interconnections 51 makes it possible tocompletely planarize the surface of the insulating film 53 and, at thesame time, to decrease the thickness of the TEOS silicon oxide film andreduce the CMP polishing amount.

In a similar manner to Embodiment 1, second and third interconnectionlayers are then formed, whereby the DRAM of Embodiment 3 is almostcompleted. According to the fabrication process of Embodiment 3, thecomplete planarization of the insulating film of each of the layers canbe attained and at the same time, the step load can be reduced.

Also in this Embodiment 3, dummy members can be disposed in the scribingarea, but not at the peripheries of the bonding pad and marker, asillustrated in connection with Embodiments 1 or 2. In addition, it ispossible to not dispose the dummy members at the periphery of the regionin which a fuse is formed. Moreover, it is needless to say that thedummy gate interconnections 34 as described in Embodiment 3 can bedisposed in the semiconductor integrated circuit device of Embodiments 1or 2.

(Embodiment 4)

FIG. 23 is a cross-sectional view illustrating one example of asemiconductor integrated circuit device according to Embodiment 4. Thesemiconductor integrated circuit device according to Embodiment 4 hasdummy regions 60 formed in an element isolation region D,3 which definesan active region 4 of a semiconductor substrate 1. In other words, thedummy regions (dummy members) 60 are formed in the wide elementisolation region D. Since elements and interconnections on thesemiconductor substrate, except for the element isolation structure, aresimilar to those of Embodiment 1, a description thereof will be omitted.The dummy regions 60 may be formed in a scribing area, and they aredisposed under similar conditions to those in Embodiment 1 concerningthe dummy interconnections it. The dummy regions 60 have been formed asdescribed above so that, upon the formation of the element isolationregion D,3 by the CMP method, no dishing occurs in the element isolationregion D,3 and therefore, the planarization of the surface of thesemiconductor substrate 1 can be attained. In addition, by decreasingthe size of the dummy regions 60 and optimizing the number of them, arise in the parasitic capacitance attributable to the existence of thedummy regions 60 can be prevented, whereby the performance of thesemiconductor integrated circuit device can be maintained.

Incidentally, in a region where gate interconnections 6 are to beformed, on the principal surface of the semiconductor substrate 1, it isnot recommended to dispose the dummy regions 60. In other words, belowthe gate interconnections 6, a prohibited area 70 is provided in whichno dummy region 60 is disposed. Such a state is illustrated in FIGS. 24and 31. The dummy regions 60 have the same effects with the activeregion 4 of the semiconductor substrate 1. When the gate interconnection6 is formed right above the dummy region 60, the gate interconnection 6and the active region 4 become opposed to each other through the gateinsulating film 5 and the parasitic capacitance of the gateinterconnection 6 increases. When the dummy regions 60 are not disposedin the area where the gate interconnection 6 is to be formed, on theother hand, the parasitic capacitance of the gate interconnection 6 doesnot show an increase. As a result, such a constitution prevents thedeterioration in the performance of the semiconductor integrated circuitdevice. In this Embodiment, the dummy regions 60 each has a quadrateshape having as width (a) and length (b), about 15 to 20 μm. ThisEmbodiment is not limited to the use of a quadrate shape, but anothershape, such as a square, also can be employed.

A description will next be made of the fabrication process of thesemiconductor integrated circuit device according to Embodiment 4 withreference to FIGS. 25 to 28.

As illustrated in FIG. 25, a silicon nitride film 61 is deposited on theprincipal surface of the semiconductor substrate 1, followed by thepatterning of the silicon nitride film 61 and the semiconductorsubstrate 1 to form shallow trenches 2. The shallow trenches 2 includeboth those which will be element isolation regions D,3 and those whichare dummy regions 60. In other words, the shallow trenches 2 are formedso that the dummy regions 60 are disposed in the element isolationregion D,3 which defines the active region 4.

As illustrated in FIG. 26, a silicon oxide film is deposited, forexample, by the CVD method. As a first polishing, the resulting film ispolished by the CMP method and embedded in the shallow trench 2, wherebythe element isolation region D,3 and dummy regions 60 are formed. Forthe first polishing, an alkaline slurry containing silicon oxideparticles as an abrasive can be employed. In this case, it is necessaryto form the silicon oxide film to a certain thickness because a ratio ofthe polishing rate of the silicon oxide film to that of the siliconnitride film becomes 3 to 4:1.

As illustrated in FIG. 27, secondary polishing is carried out to removeforeign matter and the damaged layer. For secondary polishing, either asoft pad or a chemical solution may be used. Instead, pure water mayalso be used. Then, both sides of the semiconductor substrate 1 arescrubbed and washed with hydrofluoric acid, followed by washing withammonia and then hydrochloric acid. Then, the element isolation regions3 and dummy regions 60 are etched back. The etchback can be effectedeither by dry etching or wet etching. By the etchback of the elementisolation regions 3 and dummy regions 60 as described above, theirheights can be made equal or lower than that of the active region, whichmakes it possible to carry out minute processing of a gateinterconnection.

In the final step, the silicon nitride film 61 is removed, whereby thesemiconductor substrate 1 as illustrated in FIG. 28 having the elementisolation region D,3, which defines the active region 4, formed thereonis prepared. A description of the subsequent steps will be omittedbecause they are similar to those of embodiment I.

Incidentally, the first polishing can be conducted using a slurrycontaining cerium oxide as an abrasive. In this case, the ratio of thepolishing rate of the silicon oxide film to that of the silicon nitridefilm falls within a range of from 30–50 to 1, whereby the thickness ofthe silicon nitride film 61 can be suppressed to 50 nm or less. Sincesuch a small thickness is negligible in the process design, theabove-described etchback of the element isolation regions 3 and thedummy regions 60 can be omitted, leading to a simplification of theprocess.

The present invention made by the present inventors has been describedabove specifically based on some embodiments. It should however be bornein mind that the present invention is not limited to the specificembodiments. It is needless to say that various changes andmodifications can be made so long as they do not depart from the essenceof the invention.

For example, in the above Embodiments 1 to 4, the CMP step serves as astep for polishing an insulating film. The present invention makes itpossible to secure flatness to some extent prior to the CMP polishing sothat the CMP polishing can be employed as a finishing step. In thiscase, not only the CMP method, but also dry-belt polishing or lappingmethod, can be adopted as the finishing step.

As illustrated in FIG. 32, the dummy gate interconnections 34 as shownin Embodiment 3 may be disposed in Embodiment 4. FIG. 33 is afragmentary plan view of FIG. 32. Dummy gate interconnections 34 areconstituted so that they extend over element isolation regions D,3 anddummy regions 60. Each of the dummy gate interconnections 34 is formedon the dummy region 60 thorough a gate insulating film 5 under theelectrically floating state.

By ion implantation using as a mask a resist film covering the elementisolation region D,3 upon the formation of a semiconductor region 8,which is to be a source and drain region for the MISFETQ1, impuritiesare not introduced into each of the dummy regions 60 and a semiconductorregion 8 is not formed in this region.

As illustrated in FIG. 34, the dummy gate interconnections 34 may beformed to be slender over the interconnection as illustrated in FIG. 34,which makes it possible to improve the flatness of the surface of theinsulting film.

The dummy gate interconnections 34 may be formed to extend only over theelement isolation region 3 and not to extend over the dummy regions 60,so that the capacitance between the substrate I and the dummy gateinterconnections 34 is decreased. Incidentally, it is needless to saythat the dummy regions 60 as is shown in this Embodiment can be employedin Embodiment 3.

The advantages available by the typical embodiments, among thosedisclosed herein, will hereinafter be described simply.

The surface of a member after polishing by the CMP method can beplanarized completely.

The process margin in the photolithography step, etching step and thelike can be heightened, a demand for minute processing and integrationheightening can be satisfied, and the reliability and yield of thesemiconductor integrated circuit device can be improved.

The process can be started easily.

The amount of polishing of the member to be polished by the CMP methodcan be reduced, which decreases the load and time of the step, leadingto an improvement in the cost competitive advantage.

A method of designing a member pattern permitting the completeplanarization by the CMP method can be provided.

An increase in the parasitic capacitance of interconnections or thelike, which is derived from the measures to actualize the completeplanarization, can be suppressed, whereby the performance of thesemiconductor integrated circuit device can be maintained.

1. A method of manufacturing a semiconductor integrated circuit device,comprising steps of: forming trenches in a semiconductor substrate suchthat said trenches defines active regions and dummy regions notfunctioning as a semiconductor element; forming a first insulating filmover said trenches; filling said first insulating film in said trenchesby polishing said first insulating film to form element isolationinsulating films filled in said trenches; forming semiconductor elementson said active regions; forming a second insulating film over saidsemiconductor elements; and polishing said second insulating film,forming dummy interconnections over said second insulating film suchthat said dummy interconnections do not function as an element; forminga third insulating film over said dummy interconnections; and polishingsaid third insulating film, wherein said dummy regions and said dummyinterconnections are regularly arranged at a scribing area,respectively.
 2. A method of manufacturing a semiconductor integratedcircuit device according to claim 1, wherein said dummy interconnectionis formed by the same level layer as interconnections functioning as bitlines of a dynamic random access memory.
 3. A method of manufacturing asemiconductor integrated circuit device according to claim 1, whereinsaid dummy interconnections are formed over said dummy regions.